Field of the Invention
This invention relates to systems and methods for enabling point-in-time-copy target volumes to be primary volumes in cascaded data replication systems.
Background of the Invention
In data replication environments such as Peer-to-Peer-Remote-Copy (“PPRC”) environments, data is mirrored from a primary storage device to a secondary storage device to maintain two identical copies of the data. The primary and secondary storage devices may be located up to several hundred kilometers from one another. In the event the primary storage device fails, I/O may be redirected to the secondary storage device, thereby enabling continuous data availability. In certain implementations, additional storage devices may be added to the data replication environment to create a cascade of storage devices. For example, a third storage device, possibly at a third site, may be linked (either synchronously or asynchronously) to the secondary storage device to create a third copy of the data. This third copy may be desired in situations where the primary and secondary storage devices have experienced failures or issues with data integrity. In such configurations, the secondary storage device may act as the primary storage device as it relates to the third storage device.
In certain cases, a user may wish to create point-in-time copies (e.g., FlashCopies) of volumes on each of the storage devices that are arranged in a cascade. These point-in-time copies may be used to recover data to a desired point in time. This may be needed, for example, in the event a batch job or other operation fails, or data is corrupted and needs to be restored. The point-in-time copies may also be used in test environments. Users may desire to maintain consistent point-in-time copies on remotely located storage devices for backup and/or testing purposes.
Currently, a volume that is a target in a point-in-time-copy relationship cannot be the primary in a PPRC relationship if the secondary of that PPRC relationship is itself also a primary in a PPRC relationship, as may occur in a cascaded configuration of three or more storage devices, as described above. Stated otherwise, a point-in-time-copy target volume cannot typically be a primary volume in a cascaded data replication system.
In view of the foregoing, what are needed are systems and methods to enable point-in-time-copy target volumes to be primary volumes in cascaded data replication systems.